1. Field of the Invention
This invention relates to an implantable system for stimulating electrically excitable tissue within a patient and more particularly relates to such a system in which the stimulating electrodes are selectable while minimizing the number of conductors within the lead.
2. Description of the Related Art
Often it is desirable with spinal cord or deep brain stimulation for pain relief or control of movement disorders to have many stimulation electrodes on a stimulation lead in order to place one or more cathodes and one or more anodes in optimal locations to produce benefits or minimize undesirable side effects. Implanted systems now use one to three leads and have between one and sixteen stimulation electrodes. Such systems typically must pass up to 20 milliamperes of current or more, involving current densities of 10 microcoulombs per square centimeter per phase or more. As a result, each electrode is connected to a sizable conductor in order to minimize energy losses due to impedance and to provide adequate strength to connect the wire to a power supply without substantial risk of breakage. Most current systems have the ability to program the polarity of each electrode. Due to size limitations and properties of conductors, it is difficult to have high reliability when there are eight, sixteen or more wires within a lead body that is implanted in a patient.
A lead with twenty to fifty or more stimulation electrodes could be useful for some therapies. Optimal combinations of cathodes and anodes could be selected for each patient. However, the use of this many electrodes has not been feasible in the past because of the size limitations imposed by the need to have a sizable conductor connected to each electrode. The present invention is directed to solving this problem.
A tripole lead is shown in PCT Publication No. WO95/19804 (Jul. 27, 1995), which is incorporated herein by reference in its entirety. However, such a lead lacks the ability to reprogram electrodes, and clinical benefit is critically dependent on electrode positioning. U.S. Pat. Nos. 5,713,922 and 5,925,070 disclose a system for adjusting the locus of excitation of tissue using two or three electrical leads, however, such systems are limited in the range of adjustment that can be made. Both of these patents are incorporated herein by reference in their entireties. This invention overcomes the disadvantages of the foregoing lead by allowing changes in an effective stimulation area after implant by programming.
An additional shortcoming of prior art nuerostimulation paddle leads is that they require implantation via invasive surgery. Accordingly, there is a need for a percutaneous lead that does not require implantation via invasive surgery.
The invention is useful for interacting with electrically excitable tissue of a patient. According to a preferred embodiment, a group of implantable electrodes is adapted to interact with the tissue. A main cable extends from a first site to a second site adjacent the tissue. A source of data identifies one or more of the electrodes within the group, and a data conductor extends from the source of data to the second site. An implantable controller is responsive to the data for gating one or more of the electrodes to the main cable.
The invention enables electrical signals to be transmitted between the first site and one or more selectable electrodes within the patient with a minimum number of conductors. As a result, the number of electrodes implanted in the patient can be substantially increased in order to provide improved therapeutic effects. By minimizing the number of conductors, reliability is improved.
According to another embodiment of the invention, the electrodes include both recording electrodes and stimulating electrodes.
In another embodiment, the present invention is a multi-electrode percutaneous lead that allows stimulation from any one of a number of electrodes with the use of three or fewer conductors to the signal generator.